A cable using a composite material of high strength fiber and thermosetting resin as a material has properties such as high strength, low elasticity, lightweight, high corrosion resistance, high fatigue resistance, and non-magnetic property. Therefore, it is increasingly applied to various fields as a material to replace a usual steel rope or strand cable, and a PC tendon member.
There are various kinds in such a cable made of the high strength fiber composite material, and in reinforcing means of a large structure requiring high tension such as a cable for preventing deformation of a large roof, a tension tendon member of a main girder of a bridge, an outer cable of a main girder of a bridge, a stay cable of a cable stayed bridge, a main cable of a suspension bridge, or a ground anchor, a “multilayer twist structure cable” formed by lapping element wires s including high strength fiber compounded with thermosetting resin in multiple layers and twisting them together as in FIG. 1(a), or a “bundle structure cable” formed by bundling several unit cables k in parallel with an appropriate interval being kept from one another, the unit cable being formed by collectively twisting the element wires including high strength fiber compounded with resin, as in FIG. 1(b).
However, there have been the following drawbacks in such a usual cable made of the high strength fiber composite material.
First, in the former multilayer twist structure cable, element wires are in a line contact relationship to one another, and a section of the cable is in an approximately circular shape, consequently surface area is small. Therefore, when an end anchoring portion is provided for connecting the cable to another object or adding tension, sufficient anchoring efficiency is hardly obtained even if resin or cement is poured into a sleeve and solidified in order to unify the sleeve and the cable, and complicated operation of breaking a cable end into respective element wires is necessary to obtain sufficient adhesion.
Moreover, since the multilayer twist structure cable is in a configuration where all element wires are twisted together in an S or Z direction, equipment for twisting becomes larger with increase in number of element wires, leading to significant increase in equipment cost and operation cost.
In the latter parallel bundle structure cable, when respective unit cables are not uniform in length, or when the cable is disposed with being bent by a deflection portion or the like, tension is not evenly transmitted to each of unit cables in introducing tension into the cable, consequently originally designed tension of the cable may not be achieved.
Moreover, when the cable is wound on a reel to carry the cable, shape deformation occurs, therefore handling is difficult, in addition, bending stress acts due to difference in diameter between the inside and the outside of the cable, consequently the cable may be damaged.
Furthermore, since the cable is simply formed by evenly drawing the unit cables in parallel, it is weak against torsion, and in particular, when it is distorted in a direction opposite to a twist direction of the unit cables, element wires configuring the unit cables are spaced from one another, leading to damage of the cable. In addition, the cable is fatally weak against compression (buckling) in an axial direction.
Moreover, in the case that a cylindrical body is attached on the periphery of the cable, and resin or cement is filled into the cylindrical body so that the cable and the cylindrical body are unified to obtain an anchoring portion, or the case that a sheath tube storing the cable is filled with a specific gravity regulator to use the cable as a ground anchor, filler inevitably flows out to the outside through gaps between element wires of the unit cables or gaps between the unit cables, therefore complicated treatment is necessary to fill the gaps.